Yes, you are 100% right.
Cracking password of any document, whether a simple MS word, .pdf or a compressed file like .zip or .rar, is quite tricky and time consuming as all of them depend on brute force technique along with use of dictionary and algorithm/ some logic techniques to the extent possible. The success rate, therefore is relatively low even if one waits patiently for a long time and it also depends on the complexity of the password used. Unfortunately, except for these password crackers, there is no other method available to crack the unknown/ forgotten password. Some of the available MS word password crackers are:
1) SysTools Word Password Recovery Tool;
2) eSoftTools Word Password Recovery Software;
3) Passper for Word
4) John the Ripper
All of these require a desktop or laptop and cannot be done on a mobile.